1. Field of the Invention
The present invention relates to pistons for disc brakes, and more particularly to a piston which provides a first modulus of elastic deflection throughout a first range of force transmission and a second higher modulus of elastic deflection for a second range of force transmission therethrough.
2. Description of the Related Art
The use of disc brakes in motor vehicles has become extensive. Pistons for reciprocation in calipers of motor vehicle disc brakes have been fabricated from a range of materials including steel and, more recently, plastic (polymeric) materials such as phenolic resin molding compound. Such pistons may be produced by molding techniques known in the art. Typical plastic pistons are described in U.S. Pat. No. 4,170,926. In such applications, a plastic piston is used to transmit a force acting as a hydraulic pressure on one end face thereof to a backing plate maintained in contact with the opposing face surface thereof. As such, the entirety of brake force is transmitted through the material of which the piston is constructed. Deformation of the piston due to the modulus of elasticity of the material the piston is constructed of can provide a deflection in the braking system. In some instances this deflection may be beneficial as it manifests itself as driver feel. However, in emergency stop conditions, the piston may be excessively deformed and/or the elastic range of deformation may be exceeded causing the brake piston to be deformed. Therefore, there is a need to provide a brake piston which is elastically deformable over a certain range of force transmissions with a structural limit of deformation present for the purpose of preventing the piston from being excessively deformed during high force brake applications.